This application claims the priority of German Patent Document 100 35 334.7, filed Jul. 20, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to the skin of an airplane door, which conforms to the surrounding surface contour of the fuselage, which is connected with a door frame, which door frame has supports arranged in the longitudinal direction of the fuselage and spaced with respect to one another in the circumferential direction, and which during the flight is exposed to a pressure load direction.
In the closed position, the skin of an airplane door conforms to the surface contour of the fuselage which surrounds it. The skin corresponds to the outer wall of the door. It essentially has a constant material thickness and seals off the door opening in the closed position and, without any transition, conforms to the surface contour of the fuselage. It is therefore uniformly curved in the circumferential direction and has no elevations or indentations. Recessed grips are covered.
The normal form of the skin of an airplane door corresponds to the original form of the skin, as manufactured. The skin exhibits its normal shape before and after the landing of the airplane.
The skin of the airplane door is fastened on supports which are arranged horizontally along the door width. The supports are therefore aligned in the longitudinal direction of the fuselage. These supports are spaced with respect to one another in the circumferential direction and are fixedly connected with the skin. Bearing elements, which rest on stop devices of the fuselage-side frame when the door is in the closed position, are arranged at the ends of the supports. These bearing elements make it possible that the supports of the door can be supported against a pressure load direction in the frame of the fuselage, and they prevent that, in the closed position, the door can change its position in the radial direction. The skin of the airplane door forms a portion of the outer surface of the airplane. On the door side toward the airplane cabin, the supports are covered with a planking.
The skin forms a so-called bearing area which has to absorb and transmit pressure loads and aerodynamic loads, while the inside planking is part of the so-called non-bearing area because a considerably lower stressing takes place there than on the skin.
After the start of the airplane, the pressure relationships between the airplane cabin and the outer atmosphere of the airplane change increasingly. While, inside the cabin, the pressure corresponds essentially to a known normal atmospheric pressure, the outside pressure will fall as the lift increases. This pressure difference between the airplane cabin and the atmospheric environment of the airplane results in an increasing pressure load upon the airplane door. This is increased by aerodynamic loads by atmospheric oncoming flows and whirls.
These pressure loads are absorbed by the door structure, are transmitted to the frame of the door and are transmitted from there, by way of the coupling of the bearing element and the stop element, onto the fuselage structure of the airplane.
Particularly the pressure load sucks the skin of the airplane door out of the fuselage position radially to the outside. The pressure loads applied to the door act in the direction of the pressure gradient, thus from the fuselage interior essentially in the direction toward the outside of the fuselage. Because of the elasticity of the bearing elements as well as of the stop devices, a very slight displacement of the entire door takes place in the radial direction.
However, there is also a displacement, that is, an arching-out, of the skin of the airplane door in the direction of the pressure drop. According to the existing regulations, such displacements on the skin of an airplane door may maximally have a defined value with respect to the normal shape of the skin.
Although they are relatively slight, these displacements, that is, archings, cause swirls which disadvantageously influence the flow resistance. This influences the fuel consumption of the airplane in a measurable manner.
This demand for slight reliable displacements on the skin is met in that the door receives a sufficient stiffness. This is achieved by the supports and in that the skin of the airplane door is dimensioned correspondingly thick and the door is disposed in a separate bearing with respect to the frame. This high stiffness of the door has the disadvantage that a light-weight construction of the previous door is not possible. In this case, the skin causes approximately 25% of the entire door weight.
It is an object of the invention to clearly reduce the dimension of the skin of an airplane door with a view to a light construction and in the process, if possible, avoid displacements on the skin.
The object is achieved by providing a skin of an airplane door, which conforms to the surrounding surface contour of the fuselage, which is connected with a door frame, which door frame has supports arranged in the longitudinal direction of the fuselage and spaced with respect to one another in the circumferential direction, and which during the flight is exposed to a pressure load direction, characterized in that a skin preformed against the pressure load direction is connected with supports of the door frame. The skin is preformed against the pressure load direction, and this preformed skin is connected with supports of the door frame. At cruising altitude, a pressure load to the skin takes place which has the result that the skin fits fluidically advantageously into the surface contour of the fuselage surrounding it. The resulting displacements are compensated by the preformed skin and cannot disadvantageously influence the flow resistance of the skin. This leads to measurable savings of fuel during the flight. By means of the invention, it is possible with respect to a material to construct the skin in a smaller thickness than in the case of known doors; disturbing displacements on the skin would nevertheless essentially be avoided. The invention thus permits a reduction of weight. By means of less material for the skin, clearly better characteristics of the door are achieved while the manufacturing expenditures are essentially the same.
According to an embodiment of the invention, it is advantageous to arch the skin in a center area along the longitudinal axis in an essentially concave fashion and to form an edge which is arched in the direction of the interior of the fuselage. Qualitatively, the profile of a preforming along the door width corresponds essentially to the indicated course of the curve Vv(b). The point-focally different values of a preforming are a function of the material of the thickness of the skin and also of the geometry of the door.
In the case of a door cast in one piece, it is expedient to mill the preformed surface contour on the exterior side of the skin. In the case of a skin produced from a fiber composite, the preformed surface contour is achieved by means of the lamination.